The Environment Ministry expects to get a preliminary closure study on the Tiwai Pt aluminium smelter by the end of the year.
Rio Tinto has promised to shift more than 200,000 tonnes of the most toxic spent cell liner waste from the smelter. (File image) Photo:
The government has made a clean-up of the polluted site a bottom line for when operations close at the end of 2024, but lacks the legal teeth to enforce this.
The ministry said it understood smelter majority owner Rio Tinto would undertake remediation, including removing some material, by early 2024 when it was expected to deliver its final closure study.
Rio Tinto has promised to shift more than 200,000 tonnes of the most toxic spent cell liner waste, though it has not said where to.
OIA documents show previously Rio Tinto had been trying to find a local disposal option rather than exporting the waste, which is becoming more difficult.
Commitments about Tiwai's giant landfill have been harder to come by.
It recently released hundreds of pages of contamination tests, which have been hugely expanded to cover much more of the site, that borders Department of Conservation land and is in a fragile coastal ecosystem.
These show the primary contaminants in groundwater are aluminium and fluoride, and in soil are aluminium, polycyclic aromatic hydrocarbons and fluoride, and to a lesser extent arsenic, vanadium, lead, and total petroleum hydrocarbons.
"There are multiple soil exceedances of the applicable human health criteria for industrial and recreational land uses," said a 949-page report.
However, it noted that cyanide, asbestos and PFAS - so-called "forever" chemicals - did not exceed key thresholds.
The government was forced last year to spend at least $2m on external legal advice because the issues were "extremely complex" with "significant" risks for setting precedents for how other industrial pollution was dealt with, OIA documents showed.
These reveal months of fraught positioning during talks that collapsed in March this year, with officials expressing fears the Crown might not be able to reduce its "significant liabilities in relation to the smelter's closure".
At one stage, the government moved to review "the legal options" around the "personal liability" of directors of New Zealand Aluminium Smelters (NZAS).
Rio Tinto rejected a government offer of a multi-million dollar payment that would have required it to spend at least $300m on cleaning up, but agreed to keep the smelter open for three more years after it secured a deal for cheaper power with Meridian.